HRP20031006A2 - Method for assigning frequencies to base stations of a mobile telephone network - Google Patents

Abstract

The invention relates to a method for allocating frequencies to base stations in a mobile telephone network, especially a method for automatically resetting frequencies already allocated in the case of non-saturated base stations and re-allocating frequencies to said base stations. Firstly, frequencies are allocated to base stations using any known prior art method. In the case where no non-saturated base station is present, a complete frequency plan is obtained. However, if some base stations are not saturated, the inventive method is carried out: the current frequency allocation is reset and a new frequency allocation is carried out automatically. A parameter, the resetting extent parameter, is used to determine to which extent the resetting method is implemented.

Description

The invention relates to a procedure for assigning frequencies to base stations of a mobile radio network, and in particular to a procedure for automatically returning already assigned frequencies in case of unsaturated base stations and reassigning frequencies to base stations.

In the work on the expansion of the existing mobile radio network, for example by connecting new base stations, after assigning frequencies, which is usually carried out by a process supported by EDV, it may happen that some newly connected base stations are not saturated. This means that base stations (power) will be assigned frequencies less than necessary.

In principle, there are two reasons why these base stations are unsaturated after the frequency allocation procedure. On the one hand, it can be about base stations for which, due to the structure of the network, depending on the planning parameters, saturation cannot be achieved, and on the other hand, it can be about base stations that, due to the earlier assignment of frequencies to "old" base stations, cannot be assigned the desired number of undisturbed frequencies. For the second case, there is a possibility in principle to achieve saturation of the basic stations, whereby the "old" frequency assignments are rearranged, so that after that it is possible to assign frequencies to the newly connected stations. Until now, radio network planners have implemented this second option manually. Manual post-processing requires not only the identification of cells, which prevent the assignment, but also the finding of the optimal new frequency assignment.

The task of the proposed invention is to provide a procedure that automatically assigns the corresponding necessary frequencies to unsaturated base cells if possible.

This task is solved with the features mentioned in the first patent application.

Favorable and further embodiments of the procedure are given in the dependent patent claims.

The procedure is primarily carried out in the form of a software package.

The advantage of the described procedure is that it independently recognizes the base stations whose frequencies prevent new allocations and

- makes those existing allocations available again,

- automatically replaces previously made frequency assignments with new frequencies,

- assigns frequencies to initially unsaturated basic cells.

This makes the work of the radio network planner much easier, because the entire procedure takes place automatically and manual frequency assignment is no longer necessary.

An exemplary embodiment of the invention will be described below in more detail with the help of drawings. At the same time, further features, advantages and possibilities of application of the procedure are seen.

On the drawings:

Figure 1 shows the flow of the frequency assignment function with automatic reassignment and reassignment;

Figure 2 shows the different backhaul depths (ring depths) on a single cellular mobile radio network.

In the case of frequency assignment, the aim is to assign frequencies to base stations (BS). The assignment must meet certain conditions that mainly serve to reduce interference in the mobile radio network.

As a rule, one BS needs more than one frequency. Frequencies required for one base station are given priority in the prefield. Frequencies are assigned to base stations in the order of their priority. The highest priority frequencies are assigned to important control channels (eg BCCH: Broadcast Control Channel). They are followed by second priority frequencies for traffic channels (TCH: Traffic Channel) and third priority frequencies for other channels (eg HTCH).

Example: The base station needs four frequencies. Then the prioritization may look like the following. A base station needs a priority 1 frequency, one priority 2 frequency and two priority 3 frequencies.

In this case, the base station is assigned only one frequency of priority 1. If the assignment is successful, i.e. the frequency can be assigned to the base station (BS), then the base station BS is assigned one frequency of priority 2. Then, if the frequency assignment with priority 2 if successful, the base station, BS, is assigned two priority 3 frequencies.

Then, frequencies with different priorities are generally marked with P1 (priority 1), P2, P3, etc. In principle, priority 1 frequencies must be assigned before frequencies with priority 2, etc.

The functional flow is shown in Figure 1. The first step is to assign a frequency using any procedure known from the state of the art. If there are no unsaturated base stations, a complete frequency plan is obtained.

However, if there are unsaturated base stations, then the procedure according to the invention is carried out, i.e. the previous frequency assignment is restored and then the frequencies are automatically reassigned. The extent to which the restore procedure will be carried out is managed, among other things, depending on the parameter, the restore depth parameter.

The basic principle of the frequency restoration procedure consists mainly of four stages:

Stage 1: First, it is checked whether the gap of the connection prevents the saturation of the cell. If this is the case, the corresponding frequencies are returned and new ones are assigned, so that the saturation level of the cell is increased. The distance between the connection means the distance between the frequencies used at the base station. By determining the connection distance, strong interference between frequencies can be prevented.

Example: A station has frequency 16 assigned as a P1 frequency and it needs another P2 frequency. Available amounts of frequencies (14, 15, 16, 17, 18}, the connection distance can be equal to 3. All frequencies are in principle permissible, as well as P1, and also as P2 frequency. However, frequencies 14, 15, 17 and 18 are cannot be assigned due to the junction gap as the P2 frequency. Therefore no P2 frequency can be assigned to the cell. However, by rearranging the P1 frequency from 16 to 14, it is possible to assign frequency 17 as the P2 frequency. The cells are then assigned frequencies 14 and 17 as P1, or P2 frequencies.

Stage 2: If the first stage was not successful, i.e. no P2 frequency can be assigned to the base station in that stage, then in the second stage it is checked whether - depending on the type of assignment - Pn+1, Pn+2, Pn+3 etc. frequency has quality requirements for Pn frequency, ie, higher priority frequencies. If this is the case, the corresponding frequency is rearranged. For example P2 frequency is raised to P1 frequency. If possible, the rearranged frequency is reassigned. It is generally true that the Pn frequency can be most advantageously rearranged to the Pn-1, Pn-2, ..., P1 frequency.

Example: Given a station that was assigned frequency 16 as P2 frequency. The station needs another P1 frequency. The amount of frequencies allowed may be (14, 15, 16, 17, 18), the link spacing may be 3. Frequencies 14, 15, 17 and 18 may be unassigned to the observed base station due to assignments by other stations. If frequency 16 also has P1 quality, then it is rearranged for P1 frequency. Then the BS no longer has any P2 frequencies in any case. If one further frequency were given, which would be assigned to the station as the P2 frequency, then the procedure would additionally assign it. The BS would then also have one P2 frequency.

Stage 3: If the previous stage was not successful, then frequencies are restored on stations which have a direct interference relationship with the current station and which prevent assignment on the current station.

Figure 2 shows a schematic section of a cellular mobile radio network consisting of a large number of radio stations 1, 2, 3, which in each case receive radio signals from at least one base station (which is not shown individually. The base stations are in an interference relationship with each other , where the immediately adjacent base station 2 to base station 1 is usually in a direct interference relationship with the observed base station, while further, distant base stations 3 usually have only an indirect interference relationship with base station 1.

If the observed station 1 cannot be assigned the requested frequency only due to interference relations that are in pairs, then the frequencies are returned to stations 2, which prevented the corresponding assignment. This is done by the algorithm, if replacement frequencies can already be assigned on the stations where the handover is performed. It is said to return to return depth 1 (annular depth 1).

Example: Station A is given, which needs one P1 frequency. The number of frequencies can be (14, 15, 16, 17, 18) and the connection distance is 3. Frequencies 14 and 18 cannot be assigned due to the obligation to coordinate those stations. The obligation to coordinate means restrictions on choice and use at state borders. Disturbance station B was assigned frequency 16 as the P1 frequency. Therefore station A must not be assigned frequencies 15, 16 and 17. The restore procedure in such a case restores the P1 disturbance frequency, assigning for example frequency 16 to station A and then frequency 14 to station B. However, if no replacement can be assigned to the disturbance frequency, cell A remains still unsaturated and the returned frequency is reassigned to cell B. This example is shown graphically in table 1. The existing spectrum of frequencies is shown in individual columns. The arrays show the frequency status at stations A and B before and after the implementation of the automatic reset and reassignment.

[image]

Explanation

X: assigned BCCH frequency

C: prohibited frequency due to joint gap

L: prohibited frequency due to prohibition of coordination

N: prohibited frequency due to interference from another station

*: allowable frequency as BCCH.

Stage 4: If the previous stage was also unsuccessful and the return depth parameter is greater than 1, then the frequencies are returned to the neighboring stations 3, which prevented the assignment with an intermediate interference relationship to the observed base station 1.

In relation to the previous example, it can be said: If no frequency can be assigned to the disturbing station B due to other stations, then the frequencies of the disturbing B are restored. This is followed by the assignment of frequencies to all stations where the frequency was restored.

Figure 2 shows base stations 3 with a return depth of 2.

Allocation of frequencies is done in principle for frequency requests of the selected priority. The handover procedure considers BSs with non-saturated frequency requirements to have the same priority as frequency allocations. In any case, frequencies with a priority different from the level of frequency assignment can also be rearranged. If several valid solutions are obtained for the described stage, then the solution with the lowest number of returned frequencies is chosen. If there are several solutions with the same number of returned frequencies, then the quality of the returned frequencies decides. Pn of Pn-1 frequencies are returned first.

Claims (8)

1. A procedure for automatically restoring and reassigning frequencies to non-saturated base stations of a mobile radio network, characterized by the fact that in the first stage, it is checked whether the link gaps prevent the saturation of the base station, and if this has happened, the corresponding frequencies are returned and reassigned, that in the case where no frequency could be assigned to the base station in the previous stage, in the second stage it is examined whether - depending on the method of assignment - the Pn+1 frequency has the quality requirements for the Pn frequency, and, if this is the case, the corresponding frequency is rearranged and a new frequency assignment is made; that in the case when no frequency could be assigned to the base station in the previous stages, in the third stage the frequencies of at least one neighboring base station are returned, which have a direct interference relationship with the observed base station and which prevent the assignment of a frequency to the observed station, whereby a new assigning frequencies to the observed and neighboring base stations; that in the case when no frequency could be assigned to the base station in the previous stages, in the fourth stage the frequencies of at least one base station that prevents assignment with an indirect interference relationship to the observed base station are returned, whereby a new frequency assignment is made for the observed and for the neighboring base station. 2. The method according to claim 1, characterized in that in the case when no replacement frequency can be assigned to the neighboring base station according to the third or fourth stage, the observed base station remains still unsaturated, and the returned frequency is reassigned to the neighboring base station. 3. A method according to any preceding claim, characterized in that in the event that a neighboring base station cannot be assigned any frequency on the basis of other base stations, the respective frequencies of further neighboring base stations, which disturb the base stations, are restored, whereby then performs a new assignment of frequencies on all stations to which the frequencies will be returned. 4. The procedure according to any previous request, indicated by the fact that frequency allocation is done in principle on requests for frequencies of the selected priority. 5. The procedure according to any previous claim, characterized by the fact that the procedure of restoring base stations with unsatisfied frequency requirements is considered to have the same priority as frequency allocation. 6. The procedure according to any previous claim, characterized in that frequencies of a different priority can also be rearranged as well as those of the current level of frequency allocation. 7. The procedure according to any previous claim, indicated that in the case when several valid solutions are obtained for one of the described stages, the solution with the smallest number of returned frequencies is chosen. 8. Procedure according to any previous requirement, indicated that in the case when multiple solutions with the same number of returned frequencies are obtained, the choice of solution is decided by the quality of the returned frequencies, whereby frequencies with priority Pn have priority over frequencies of priority Pn-1.